Rheological properties of home care formulations are often managed with the use of natural or synthetic polymers. Frequently, the formulator is looking for a liquid formulation with a shear thinning viscosity profile either for aesthetic purposes of providing the impression of a thick formulation rich in actives, and/or for performance benefits such as facilitating cling to a vertical surface which might allow additional contact time for a detergent to perform its cleaning action. Some of the most commonly used polymers are high molecular weight polyacrylates, alkali swellable latex, modified celluloses, guar gum, and xanthan, all of which have found widespread use in laundry and dish liquids plus some hard surface cleaners.
While most compositions for home care have a neutral to alkaline pH, there are a couple of applications where formulas may be highly acidic. Specifically, these applications are toilet bowl cleaners and fabric softeners. In the case of toilet bowl cleaners, there is a strong interest in controlling the rheology, since cling time to the toilet bowl affects the overall performance of the product. In the case of fabric softeners, the desire to thicken the formulation is more often for aesthetics, as consumers are accustomed to fabric softener products which have a high viscosity. However, both of these products may be formulated to pHs as low as 2 or 3, and few polymers are effective at extremely low pH conditions. In the case of most polysaccharides, highly acidic conditions degrade the polymers, such that with time the viscosity may drop off significantly. Xanthan and succinoglycan gum are generally recommended for low pH formulations, but even they are not always effective at the very low pH range. Of the synthetic polymers, most are designed to viscosify at neutral to alkaline conditions, and are not effective at acidic conditions. For example, with polyacrylates and the alkali swellable latexes, low pH conditions will neutralize the carboxylic acid function, rendering the polymer often insoluble or at minimum effectiveness in low pH conditions. These thickeners also either lose their thickening property or cause precipitation of the formulation.
In addition to the potentially very low pH conditions of toilet bowl cleaners and fabric softeners, another constraint in chemistries developed for rheology management is the presence of quaternary surfactants. While laundry and dish liquid detergents are anionic surfactant based. Fabric softeners are commonly made up of ester quats, and toilet bowl cleaners may often contain quaternary surfactants for antibacterial claims. The level of quats in the two types of formulations are significantly different. Fabric softeners may contain anywhere between 10–20wt % ester quats, while quaternary ammonium type surfactants for antibacterial claim are generally added at less than 0.5 wt %. However, the consequence of the presence of quaternary surfactants in the formulation is the same for both formulations, namely, that many typical rheological modifiers will be incompatible due to their anionic charge.
Polymers, and especially copolymers, comprising cationic units are useful in various applications. In formulations, for example in home care formulations, personal care formulations, or formulations used in oil-field industry, the cationic units may interact with other compounds, such as surfaces, surfactants or active ingredients, and provide specific properties. Various polymers and copolymers comprising cationic units are used. Some properties and/or structures of formulation can be tuned by using copolymers comprising several cationic units. Developing new monomers and therefore new polymers or copolymers allows for development of new formulations with either environment protection improvements, or of course new and improved properties or functions.
Copolymers comprising units that comprise two cationic groups (hereafter referred to as di-cationic units), and preparation thereof, have been described, and are used for example in home care formulations such as hard surface cleaning formulations.
Hydrophobic modified cationic monomers have been described by Gipson et al,1 and reported recently by Joynes et al2. These are surfactant monomers that can be copolymerized, imparting the polymer with both the cationicity and hydrophobicity. Diquaternary monomer without hydrophobes was prepared by Dammann3. It is enviable that a hydrophobically modified diquaternary and multi-quaternary monomers would provide its polymer or its copolymer unique properties, such as complex formation with surfactants and/or self-association as thickeners. 1 Gipson, R. M.; Hotchkiss, P.; Nieh, E. C. Y. (Texaco) U.S. Pat. No. 4,212,820 (1980)2 Joynes, D.; Sherrington, D. C. Polymer, 37(8), 1453, 19963 Dammann, L. G. (Celanese) U.S. Pat. No. 4,495,367 (1985)
There is an increasing demand for thickeners in acidic compositions and/or compositions of mostly cationic surfactants. There are few examples of thickeners for acidic media published in the literature and/or commercially available. For example, U.S. Pat. No. 6,326,430 describes a cross-linked poly(methacryloxyethyltrimethylammonium) salt as thickening agent for aqueous laundry softeners which comprise cationic surfactants as active ingredients and toilet cleaners4. The polymer was synthesized in w/o emulsion and cross-linked with N,N′-methylenebisacrylamide. Similar polymers were also described in various patents.5 Separately, U.S. Pat. No. 6,271,192 describes a thickener latex of a polymer from ethyl acrylate, dimethylaminoethyl methacrylate and an associative monomer. The latex is a microgel cross-linked by diallylphthalate.6 A similar polymer was synthesized by precipitation polymerization in an organic solvent, where a polymer microgel of dimethylaminoethyl methacrylate, vinylpyrrolidone and steryl acrylate was cross-linked by tripropylene glycol diacrylate.7 A patent was filed recently for a cross-linked hydrogel of vinylpyrrolidone and dimethylaminopropyl methacrylamide. This hydrogel was prepared by solution polymerization and was demonstrated to show thickening property upon acidification.8 4 Berte, F. U.S. Pat. No. 6,326,430 (2001). Berte, F.; Polotti, G. WO 99/20725 (1999); WO/99/06455 (1999).5 U.S. Pat. No. 3,968,0387; U.S. Pat. No. 4,806,345; EP 395,282; EP 494,554; U.S. Pat. No. 4,172,066; U.S. Pat. No. 5,114,600; U.S. Pat. No. 4,542,1756 Verstrat, D. W.; Maxim, J. S.; Rosie, J. U.S. Pat. No. 6,271,192 B17 Matsumoto, K.; Uchiyama, Y.; Kambe, T. Nanba, T. Okuda, Y. (Osaka Yuki Kagaku Kogyo Kabushiki Kaisha & Shiseido Company) U.S. Pat. No. 5,603,926 (19978 Zhong, Y.; Jachowicz, J.; Wolf, P. F. McMullen, R. L. Jr. (ISP), US2001/0016189 A1 (2001)
In summary, the cationic polymers described in the current arts as thickener for acidic formulations are almost exclusively chemically cross-linked. The cross-linking polymer network is necessary for the viscosity boost. However, the viscosity obtained is less stringy. There are still needs for better products that can thicken the acidic/cationic compositions at a low dose. It is also desirable to provide a thickening polymer that can be prepared without a cross-linking monomer. Such a polymer would have improved hydration speed and improved viscosity, i.e., less stringy.